Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Detail)	9 Months Ended
	Sep. 30, 2021 USD ($) MWh Bcf
Fixed Price - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	59	[1]
Fixed Price - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	23	[1]
Basis - Natural Gas - Current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	202
Basis - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	143
Fixed Price - Electricity - Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	14,286,444
Fixed Price - Electricity - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	5,953,983
Financial Transmission Rights - Electricity- Current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	71,265,005
Financial Transmission Rights - Electricity- Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	71,265,005
Interest Rate - Current Derivative Contract
Derivative [Line Items]
Derivative payment | $	$ 1,600,000,000	[2]
Interest Rate - Current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $	$ 850,000,000	[2]
Fixed Price - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	9	[1]
Fixed Price - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	9	[1]
Basis - Natural Gas - Non-current Derivative Contract
Derivative [Line Items]
Volume of derivative activity | Bcf	472
Basis - Natural Gas - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of derivative activity | Bcf	465
Fixed Price - Electricity - Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	32,508,487
Fixed Price - Electricity - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	6,092,512
Financial Transmission Rights - Electricity- Non-current Derivative Contract
Derivative [Line Items]
Volume of electricity | MWh	0
Financial Transmission Rights - Electricity- Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Volume of electricity | MWh	0
Interest Rate - Non-current Derivative Contract
Derivative [Line Items]
Derivative payment | $	$ 6,715,000,000	[2]
Interest Rate - Non-current Derivative Contract | Virginia Electric and Power Company
Derivative [Line Items]
Derivative payment | $	$ 1,900,000,000	[2]

[1] Includes options.

[2] Maturity is determined based on final settlement period.